Notes

Often misunderstood, this ability seems worse than Heroic Strike, but the key is the weapon used. Slam bypasses the usual melee swing timer, instead using a Channelling type bar more usually found on spells. This, in effect, gives all weapons a flat speed of 1.5 seconds (Less with talent). This is not helpful when using daggers and dual wielding, but with very large two-handed weapons, it can reduce swing times from the default, and therefore, increase DPS, drastically.

Heroic Strike, on the other hand, is 'Next Attack', which varies wildly depending on weapon.

Effective the 2.0.3 patch, Slam is no longer subject to interruption while casting. Previous to 2.0.3, Slam was interruptable in the same way as spell-caster; knocking the charge-up bar backward each time damage is taken, which can lower the DPS back to nearer normal levels.

In general though, use this instead of Heroic Strike if using two-handed weapons. If using one-handers or dual wield, stick with Heroic Strike. Also, Slam generates much less threat than Heroic, which can be useful in Secondary Tanking.

Slam is affected by the Global Cooldown though, and if you have a top-speed connection, the Global Cooldown of 1.48 seconds will thus make talent points spent in Improved Slam rather useless for PVE, if you chain-cast the spell. In pvp, however, improved slam talent allows you to get near mortal strike damage without having to stand in one place for very long.

While Slam is without a doubt a good ability, being spell with casting-time, it resets the swing timer of your weapon, and therefore you would rather use an Instant Ability like Whirlwind, Bloodthirst or Mortal Strike, if you have access to them.